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Derivative Instruments (Details 3) (Details) (USD $)
In Millions, unless otherwise specified |
3 Months Ended | |||||
|---|---|---|---|---|---|---|
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Mar. 31, 2012
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Mar. 31, 2011
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| Derivative Instruments, Gain (Loss) [Line Items] | ||||||
| Gain (Loss) on Sale of Derivatives | $ (39) | $ (36) | ||||
| Unrealized gain (loss) | 224 | [1] | (127) | [1] | ||
| Summary of Derivative Instruments by Risk Exposure [Abstract] | ||||||
| Power contracts included in operating revenues | 92 | (57) | ||||
| Natural gas contracts included in fuel and purchased energy expense | 104 | 2 | ||||
| Interest rate swaps included in interest expense | 3 | 1 | ||||
| Gain (Loss) on interest rate derivatives, net | 14 | 109 | ||||
| Gain (Loss) on Derivative Instruments, Net, Pretax | 185 | [1] | (163) | [1] | ||
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Interest Rate Swap [Member]
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| Derivative Instruments, Gain (Loss) [Line Items] | ||||||
| Gain (Loss) on Sale of Derivatives | (157) | (46) | ||||
| Unrealized gain (loss) | 146 | [1] | (62) | [1] | ||
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Commodity Option [Member]
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| Derivative Instruments, Gain (Loss) [Line Items] | ||||||
| Gain (Loss) on Sale of Derivatives | 118 | 10 | ||||
| Unrealized gain (loss) | $ 78 | [1] | $ (65) | [1] | ||
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